Pure darifenacin hydrobromide substantially free of oxidized darifenacin and salts thereof and processes for the preparation thereof

ABSTRACT

Provided are darifenacin hydrobromide free of oxidized darifenacin, and processes for the preparation thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.11/646,915, filed Dec. 27, 2006, which claims the benefit of priority toU.S. provisional application Ser. Nos. 60/754,395, filed Dec. 27, 2005;60/772,250, filed Feb. 9, 2006; 60/776,311, filed Feb. 23, 2006;60/809,147, filed May 25, 2006; 60/813,579, filed Jun. 8, 2006;60/836,557, filed Aug. 8, 2006; 60/837,407, filed Aug. 10, 2006;60/850,184, filed Oct. 5, 2006; 60/859,332, filed Nov. 15, 2006; and60/873,680, filed Dec. 7, 2006, hereby incorporated by reference. Thisapplication is also related to U.S. application Ser. Nos. 11/647,109 and11/646,919, each filed Dec. 27, 2006 and entitled “Processes forPreparing Darifenacin Hydrobromide,” hereby incorporated by reference.

FIELD OF THE INVENTION

The invention encompasses substantially pure darifenacin hydrobromidefree of oxidized darifenacin and salts thereof, and processes for thepreparation thereof.

BACKGROUND OF THE INVENTION

Darifenacin,(S)-2-{1-[2-(2,3-dihydrobenzofuran-5-yl)ethyl]-3-pyrrolidinyl}-2,2-diphenylacetamide,a compound having the chemical structure,

is a selective M3 receptor antagonist. Blockade of destructor muscleactivity manifests in an increase in urine volume that the bladder cancontain, reduction of urination frequency, and decrease in pressure andurgency associated with the urge to urinate, and thereby episodes ofincontinence are reduced.

Darifenacin is administered as the hydrobromide salt,(S)-2-{1-[2-(2,3-dihydrobenzofuran-5-yl)ethyl]-3-pyrrolidinyl}-2,2-diphenylacetamidehydrobromide, of the structure

Darifenacin hydrobromide, and is marketed under the trade name ENABLEX®by Novartis.

Darifenacin hydrobromide and three routes for its preparation aredisclosed in U.S. Pat. No. 5,096,890. The routes are illustrated by thefollowing scheme:

Darifenacin free base is purities by column chromatography on silicagel, and then converted to darifenacin hydrobromide by dissolving it inacetone and reacting with 48% hydrobromic acid.

Another process for preparing darifenacin HBr is disclosed in U.S.publication No. 2003/0191176, and is illustrated by the followingscheme:

Darifenacin free base is purified by crystallization fromacetonitrile-water mixture providing hydrate form of Darifenacin andfrom toluene providing toluene solvate of Darifenacin. Both purifieddarifenacin free base forms (hydrate or toluene solvate) are thenconverted to Darifenacin HBr by dissolving them in butan-2-one andadding 48% hydrobromic acid.

Like any synthetic compound, darifenacin hydrobromide can containextraneous compounds or impurities. These impurities may be, forexample, starting materials, by-products of the reaction, products ofside reactions, or degradation products. Impurities in darifenacinhydrobromide, or any active pharmaceutical ingredient (“API”), areundesirable and, in extreme cases, might even be harmful to a patientbeing treated with a dosage form containing the API.

The purity of an API produced in a manufacturing process is critical forcommercialization. The U.S. Food and Drug Administration (“FDA”)requires that process impurities be maintained below set limits. Forexample, in its ICH Q7A guidance for API manufacturers, the FDAspecifies the quality of raw materials that may be used, as well asacceptable process conditions, such as temperature, pressure, time, andstoichiometric ratios, including purification steps, such ascrystallization, distillation, and liquid-liquid extraction. See ICHGood Manufacturing Practice Guide for Active Pharmaceutical Ingredients,Q7A, Current Step 4 Version (Nov. 10, 2000).

The product of a chemical reaction is rarely a single compound withsufficient purity to comply with pharmaceutical standards. Side productsand by-products of the reaction and adjunct reagents used in thereaction will, in most cases, also be present in the product. At certainstages during processing of an API, such as darifenacin hydrobromide, itmust be analyzed for purity, typically, by high performance liquidchromatography (“HPLC”) or thin-layer chromatography (“TLC”), todetermine if it is suitable for continued processing and, ultimately,for use in a pharmaceutical product. The FDA requires that an API is asfree of impurities as possible, so that it is as safe as possible forclinical use. For example, the FDA recommends that the amounts of someimpurities be limited to less than 0.1 percent. See ICH GoodManufacturing Practice Guide for Active Pharmaceutical Ingredients, Q7A,Current Step 4 Version (Nov. 10, 2000).

Generally, side products, by-products, and adjunct reagents(collectively “impurities”) are identified spectroscopically and/or withanother physical method, and then associated with a peak position, suchas that in a chromatogram, or a spot on a TLC plate. See Strobel, H.A.,et al., CHEMICAL INSTRUMENTATION: A SYSTEMATIC APPROACH, 953, 3d ed.(Wiley & Sons, New York 1989). Once a particular impurity has beenassociated with a peak position, the impurity can be identified in asample by its relative position in the chromatogram, where the positionin the chromatogram is measured in minutes between injection of thesample on the column and elution of the impurity through the detector.The relative position in the chromatogram is known as the “retentiontime.”

The retention time can vary about a mean value based upon the conditionof the instrumentation, as well as many other factors. To mitigate theeffects such variations have upon accurate identification of animpurity, practitioners often use “relative retention time” (“RRT”) toidentify impurities. See supra Strobel at 922. The RRT of an impurity iscalculated by dividing the retention time of the impurity by theretention time of a reference marker. The reference marker may be theAPI in which the impurity is present, or may be another compound that iseither present in or added to the sample. A reference marker should bepresent in the sample in an amount that is sufficiently large to bedetectable, but not in an amount large enough to saturate the column.

Those skilled in the art of drug manufacturing research and developmentunderstand that a relatively pure compound can be used as a “referencestandard.” A reference standard is similar to a reference marker, exceptthat it may be used not only to identify the impurity, but also toquantify the amount of the impurity present in the sample.

A reference standard is an “external standard,” when a solution of aknown concentration of the reference standard and an unknown mixture areanalyzed separately using the same technique. See supra Strobel at 924;Snyder, L. R., et al., INTRODUCTION TO MODERN LIQUID CHROMATOGRAPHY,549, 2d ed. (John Wiley & Sons, New York 1979). The amount of theimpurity in the sample can be determined by comparing the magnitude ofthe detector response for the reference standard to that for theimpurity. See U.S. Pat. No. 6,333,198, hereby incorporated by reference.

The reference standard can also be used as an “internal standard,” i.e.,one that is directly added to the sample in a predetermined amount. Whenthe reference standard is an internal standard, a “response factor,”which compensates for differences in the sensitivity of the detector tothe impurity and the reference standard, is used to quantify the amountof the impurity in the sample. See supra Strobel at 894. For thispurpose, the reference standard is added directly to the mixture, and isknown as an “internal standard.” See supra Strobel at 925; Snyder at552.

The technique of “standard addition” can also be used to quantify theamount of the impurity. This technique is used where the sample containsan unknown detectable amount of the reference standard. In a “standardaddition,” at least two samples are prepared by adding known anddiffering amounts of the internal standard. See supra Strobel at391-393; Snyder at 571-572. The proportion of the detector response dueto the reference standard present in the sample can be determined byplotting the detector response against the amount of the referencestandard added to each of the samples, and extrapolating the plot tozero. See supra Strobel at 392, FIG. 11.4. The response of a detector inHPLC (e.g., UV detectors or refractive index detectors) can be andtypically is different for each compound eluting from the HPLC column.Response factors, as known, account for this difference in the responsesignal of the detector to different compounds eluting from the column.

As is known by those skilled in the art, the management of processimpurities is greatly enhanced by understanding their chemicalstructures and synthetic pathways, and by identifying the parametersthat influence the amount of impurities in the final product.

Thus, providing substantially pure darifenacin hydrobromide, preferably,free of oxidized Darifenacin and salts thereof, and means forpreparation thereof is beneficial.

SUMMARY OF THE INVENTION

In one embodiment, the invention encompasses darifenacin hydrobromidehaving less than 0. 1% of oxidized Darifenacin and salts thereof of thefollowing formula

wherein n is either 0 or 1 and HA is an acid. Preferably, HA is HBr.

In another embodiment, the present invention encompasses a process forpreparing darifenacin hydrobromide having less than 0.1% of oxidizedDarifenacin and salts thereof comprising a) combining3-(S)-(+)-(1-carbamoyl-1,1- diphenylmethyl)pyrrolidine tartrate or thefree base derivative of the following formula,

the compound of the following formula II,

having less than 0.25% of compound of formula I, a solvent selected fromthe group consisting of a C₆₋₉ aromatic hydrocarbon, a polar organicsolvent, water, and mixtures thereof, and a base to form a mixture; andb) admixing HBr with the mixture to obtain darifenacin hydrobromidehaving less than 0.1% of oxidized Darifenacin and salts thereof; whereinY is a leaving group selected from the group consisting of Cl , I,brosyloxy, mesyloxy, tosyloxy, trifluoroacetyloxy, andtrifluoromethansulfonyloxy.

In another embodiment, the invention encompasses a HPLC method fordetermining the presence and amount of oxidized Darifenacin and saltsthereof in a sample of darifenacin hydrobromide comprising: a) combininga sample of darifenacin hydrobromide with a mixture ofacetonitrile:water in a ratio of about 1: 1, to obtain a solution; b)injecting the solution into a column, preferably, a 150×4.6 mm×0.5 μmPhenyl C6 column; c) eluting the sample from the column using a mixtureof acetonitrile:water in a ratio of 9:1 (referred to as eluent A) andbuffer (referred to as eluent B) as an eluent; and d) measuring theoxidized darifenacin and salts thereof content in the sample with a UVdetector.

In another embodiment, the invention encompasses a compound of thefollowing formula I

wherein Y is a leaving group selected from the group consisting of Cl ,I, brosyloxy, mesyloxy, tosyloxy, trifluoroacetyloxy, andtrifluoromethansulfonyloxy.

In one embodiment, the present invention encompasses a process ofdetermining the presence of the compound of formula I in a samplecomprising the compound of formula I and the compound of formula II by aprocess comprising carrying out HPLC or TLC with the compound of formulaI as a reference marker.

In another embodiment, the present invention encompasses a process ofdetermining the amount of the compound of formula I in a samplecomprising the compound of formula I and the compound of formula II by aprocess comprising carrying out HPLC with the of formula I as areference standard.

In yet another embodiment, the invention encompasses an HPLC method fordetermining the presence and the amount of a compound of formula I

in a sample of a compound of formula II

comprising: (a) combining a sample of a derivative ofethyl-dihydrobenzofuran of formula I with a mixture ofacetonitrile:water in a ratio of about 1:1, to obtain a solution; (b)injecting the solution into a column, preferably, a 250×4.6 mm 0.5 μrmC18 column; (c) eluting the sample from the column using a mixture ofacetonitrile and buffer as an eluent; and (d) measuring the amount ofthe compound of formula I in the sample with a UV detector, wherein Y isa leaving group selected from the group consisting of Cl , I, brosyloxy,mesyloxy, tosyloxy, trifluoroacetyloxy, and trifluoromethansulfonyloxy.

In one embodiment, the invention encompasses a process for preparingdarifenacin hydrobromide having less than 0.1% of oxidized Darifenacinand salts thereof of the following formula

comprising: a) obtaining one or more samples of one of one or morebatches of a compound of formula II;

b) measuring the level of the compound of formula I

in one or more of the samples of one or more of the batches of step a);c) selecting a batch that has less than about 0.25% of the compound offormula I based upon the measurements of step b); and d) using the batchselected in step (c) to prepare the darifenacin hydrobromide having lessthan 0.1% of oxidized Darifenacin and salts thereof, wherein Y is aleaving group selected from the group consisting of Cl , I, brosyloxy,mesyloxy, tosyloxy, trifluoroacetyloxy, and trifluoromethansulfonyloxy,preferably, Cl , n is either 0 or 1, and HA is an acid. Preferably, HAis HBr.

In another embodiment, the invention encompasses a pharmaceuticalcomposition comprising darifenacin hydrobromide having less than 0.1% ofoxidized Darifenacin and salts thereof and at least one pharmaceuticallyacceptable excipient.

In another embodiment, the invention encompasses a process for preparingthe pharmaceutical composition, comprising combining darifenacinhydrobromide having less than 0.1% of oxidized darifenacin and saltsthereof and the pharmaceutically acceptable excipient.

In another embodiment, the invention encompasses a method of treatingurinary incontinence reducing urgency and increasing urine volume thatthe bladder can contain comprising administering a a therapeuticallyeffective amount of a pharmacuetical composition comprising darifenacinhydrobromide having less than 0.1% of oxidized Darifenacin and saltsthereof and at least one pharmaceutically acceptable excipient to apatient in need thereof.

In another embodiment, the invention encompasses the use of darifenacinhydrobromide having less than 0.1% of oxidized Darifenacin and saltsthereof in the manufacture of a pharmaceutical composition for thetreatment of urinary incontinence reducing urgency and increasing urinevolume that the bladder can contain.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to substantially pure Darifenacin-HBr.Especially, the invention is directed to Darifenacin-HBr free ofoxidized Darifenacin and salts thereof, as well as processes for itspreparation.

Oxidized Darifenacin and salts thereof are impurities that have beendifficult to separate from darifenacin hydrobromide by conventionalmethods because of their close structural similarity to darifenacinhydrobromide.

As used herein, unless otherwise defined, the term “free of oxidizedDarifenacin and salts thereof” when referring to darifenacinhydrobromide means darifenacin hydrobromide having very low levels ofoxidized Darifenacin and salts thereof of the following formula,

and preferably less than 0.1% of oxidized darifenacin and salts thereof;wherein n is either 0 or 1 and HA is an acid. Preferably, HA is HBr.

The level of oxidized Darifenacin and salts thereof in Darifenacinhydrobromide can be measured by w/w units. The measurement can be doneby any method known to a skilled artisan, such as an HPLC method.

The invention encompasses darifenacin hydrobromide having less than 0.1%of oxidized Darifenacin and salts thereof of the following formula

wherein n is either 0 or 1, wherein HA is an acid, preferably, HBr.Preferably, darifenacin hydrobromide has less than 0.08%, morepreferably, less than 0.05% of oxidized darifenacin and salts thereof.

When n is 0, the above formula refers to oxidized Darifenacin.

When n is 1, the above formula refers to oxidized Darifenacin salt.

When n is 1 and HA is HBr, the above formula refers to oxidizedDarifenacin HBr.

Darifenacin hydrobromide having less than 0.1% of oxidized Darifenacinand salts thereof is prepared by a process comprising a) combining3-(S)-(+)-(1-carbamoyl- 1,1-diphenylmethyl)pyrrolidine tartrate or thefree base derivative of the following formula,

the compound of the following formula II,

having less than 0.25% of the compound of formula I, a solvent selectedfrom the group consisting of a C₆₋₉ aromatic hydrocarbon, a polarorganic solvent, water, and mixtures thereof, and a base to form amixture; and b) admixing HBr with the mixture to obtain darifenacinhydrobromide having less than 0.1% of oxidized Darifenacin and saltsthereof; wherein Y is a leaving group selected from the group consistingof Cl , I, brosyloxy, mesyloxy, tosyloxy, trifluoroacetyloxy, andtrifluoromethansulfonyloxy, preferably, Cl.

Preferably, when the compound of formula II has less than 0.15% of thecompound of formula I, the obtained Darifenacin hydrobromide has lessthan 0.08% of oxidized Darifenacin and salts thereof.

More preferably, when the compound of formula II has less than 0.1% ofthe compound of formula I, the obtained Darifenacin hydrobromide hasless than 0.05% of oxidized Darifenacin and salts thereof.

Preferably, the polar aprotic organic solvent is selected from the groupconsisting of an amide, a C₁₋₁₀ halogenated aliphatic hydrocarbon, asulfoxide, an ester, a nitrile, and a ketone. A preferred amide isdimethylformamide (DMF). A preferred C₁₋₀ halogenated aliphatichydrocarbon is a C₁₋₅ halogenated aliphatic hydrocarbon, morepreferably, dichloromethane (DCM). Preferably, the sulfoxide is a C₂₋₅sulfoxide, more preferably, dimethylsulfoxide (DMSO). Preferably, theester is a C₂₋₅ ester, more preferably, ethyl acetate (EtOAc). Apreferred ketone is a C₃₋₆ ketone, more preferably, methyl ethyl ketone(MEK). Preferably, the nitrile is a C₂₄ nitrile, more preferably,acetontirile (ACN). Preferably, the C₆₋₉ aromatic is toluene or xylene.Preferred mixtures are either that of toluene and water or that of DCMand water. The more preferred solvent is water.

The base may be an inorganic base or an organic base. A preferredorganic base is selected from the group consisting of aliphatic andaromatic amines. Preferably, the aliphatic amine is triethylamine,tribytulamine, methylmorpholine, or N,N-diisopropylethyl amine.Preferably, the aromatic amine is pyridine. A preferred inorganic baseis either alkali carbonate or alkali bicarbonate. Preferably, the alkalicarbonate is sodium carbonate or potassium carbonate. Preferably, thealkali bicarbonate is either sodium bicarbonate or potassiumbicarbonate. The most preferred base is an alkali carbonate, even mostpreferably, potassium carbonate.

Preferably, the mixture is heated to a temperature of about 50° C. toabout reflux, and more preferably to a temperature of about 60° C. toabout reflux, prior to admixing with HBr. Preferably, the mixture ismaintained, under heating, for about 1 to about 5 hours, and morepreferably for about 2 to about 3 hours. After maintaining the mixture,the mixture is cooled to a temperature of about 35° C. to about 15° C.,and preferably to about 25° C. to about 15° C. Preferably, aftercooling, an organic solvent selected from the group consisting of DCM,EtOAc, and butyl acetate is added to the mixture, to give a mixturehaving an aqueous phase and an organic phase. The phases are thenseparated, and HBr is admixed with the organic phase. Preferably, HBr isadded to the organic phase.

Preferably, a small amount of an anhydride may be added to the organicphase, after separating the phases, followed by maintaining for about Ito about 3 hours. After maintaining, the organic solvent is removed, anda C₂₋₅ alcohol and hydrobromic acid are added, to obtain darifenacinhydrobromide. Preferably, the C₂₋₅ alcohol is n-butanol, sec-butanol,ethanol, 2-methyl-2-butanol, or isopropanol, more preferably, n-butanol.

Darifenacin hydrobromide having less than 0.1%, preferably, less than0.08%, more preferably, less than 0.05% of oxidized Darifenacin andsalts thereof may be recovered by removing the residual water and theorganic solvent from the acidic mixture obtained after the addition ofHBr, preferably, by distillation under vacuum, to induce precipitationof the darifenacin hydrobromide. The mixture is then cooled to roomtemperature and the resulting precipitate of darifenacin hydrobromide isseparated from the mixture by filtration.

Darifenacin hydrobromide may be further purified by crystallizing therecovered precipitate from a C₂₋₅ alcohol. The process comprisessuspending the precipitate in a C₂₋₅ alcohol, heating the suspension toa temperature sufficient to induce dissolution of the darifenacinhydrobromide, and cooling the resulting solution to inducecrystallization of the darifenacin hydrobromide. Prior to cooling, thesolution may be purified with active charcoal. The crystallized productmay be isolated by filtration, washing and drying. Preferably, the C₂₋₅alcohol is n-butanol, sec-butanol, ethanol, 2-methyl-2-butanol, orisopropanol, and more preferably n-butanol.

The presence and level of oxidized darifenacin and salts thereof in adarifenacin-HBr sample is determined by an HPLC method comprising: (a)combining a darifenacin-HBr sample with a mixture of acetonitrile:waterin a ratio of about 1:1, to obtain a solution; (b) injecting thesolution into a column, preferably, a 150×4.6 mm×0.5 μm Phenyl C6column; (c) eluting the sample from the column using a mixture ofacetonitrile:water in a ratio of 9:1 (referred to as eluent A) andbuffer (referred to as eluent B) as an eluent; and (d) measuring theoxidized darifenacin content in the sample with a WV detector.

Preferably, the buffer used in this method is a phosphate buffer. Thephosphate buffer comprises an aqueous solution of K₂HPO₄ having a pH ofabout 9.

Typically, the sample is eluted through the column by gradient elution.Preferably, the eluent is a mixture of eluent A and eluent B. Morepreferably, the sample is eluted through the column by gradient elutionunder the following conditions: At the time 0 minutes, the eluentcontains 40% of eluent A and 60% of eluent B, at 20 minutes, the eluentcontains 70% of eluent A and 30% of eluent B, and at 30 minutes, theeluent contains 70% of eluent A and 30% of eluent B.

Preferably, the presence and content of the oxidized darifenacin andsalts thereof are measured at a wavelength of 215 nm.

The invention also encompasses a compound of the of formula I;

wherein Y is a leaving group selected from the group consisting of Cl,I, brosyloxy, mesyloxy, tosyloxy, trifluoroacetyloxy, andtrifluoromethansulfonyloxy. Preferably, Y is Cl.

When Y is Cl, the compound of formula I refers to5-(2-chloroethyl)-2,3-benzofuran of the following formula.

The compound of formula I can be prepared by any method known to oneskilled in the art. Such methods include, but are not limited to, themethod disclosed in U.S. Pat. No. 5,096,890, hereby incorporated byreference. Such methods also include reacting a the compound of formulaII

with an oxidizing agent, as exemplified in example 5, or via2-(benzofuran-5-yl)ethanol of formula V.

The 2-(benzofuran-5-yl)ethanol of formula V can be produced fromcommercially available 2-(benzofuran-5-yl)acetic acid, according to anymethod known to one skilled in the art. Such methods include, but arenot limited to, converting the acid to the corresponding ester andreducing the ester to obtain the alcohol, as exemplified in examples1-3.

It is believed that oxidized Darifenacin and salts thereof are formedduring the above-described synthesis of darifenacin-HBr by reaction ofan the compound of formula I, which is an impurity often present in thestarting compound of formula II, with the starting(S)-(1-carbamoyl-1,1-diphenylmethyl)pyrrolidine of formula XI or saltthereof.

Accordingly, because separating the oxidized Darifenacin and saltsthereof from the darifenacin-HBr is difficult, a method for obtainingdarifenacin-HBr free of oxidized Darifenacin and salts thereof would beof a great advantage.

It was found that starting with compound of formula II having very lowlevels of the compound of formula I, and preferably less than 0.25% ofthe compound of formula I leads to darifenacin-HBr free of oxidizedDarifenacin and salts thereof.

The level of the compound of formula I in the compound of formula II canbe measured by area % units. The said measurement can be obtained by anymethod known to a skilled artisan, such as an HPLC method.

The compound of formula II having less than 0.25% of the compound offormula I can be prepared by the process disclosed in U.S. applicationSer. No. 11/646,919, filed December 27, 2006 and entitled “Processes forPrepared Darifenacin Hydrobromide,” wherein the starting commerciallyavailable acid analogue 2,3-dihydrobenzofuran-5-acetic acid

has less than 0.4% area by HPLC of 5-benzofuranacetic acid, providing

5-(2-hydroxyethyl)-2,3-dihydrobenzofuran of formula III

having less than 0.5% of 2-(benzoftiran-5-yl)ethanol of formula V,

and the solvent is an aromatic hydrocarbon, more preferably, C₆₋₉aromatic hydrocarbon, most preferably toluene, as exemplified inexamples 8 and 9.

The present invention encompasses a process of determining the presenceof the compound of formula I in a sample comprising the compound offormula I and the compound of formula II by a process comprisingcarrying out HPLC or TLC with the compound of formula I as a referencemarker.

The above process comprises determining the relative retention time of acompound of formula I

in a sample of a compound of formula II

by a process comprising: (a) measuring by HPLC or TLC the relativeretention time (referred to as RRT, or RRF, respectively) correspondingto a compound of formula I in a reference marker sample; (b) determiningby HPLC or TLC the relative retention time corresponding to a compoundof formula I in a sample comprising a compound of formula I and acompound of formula II; and (c) determining the relative retention timeof the compound of formula I in the sample by comparing the relativeretention time (RRT or RRF) of step (a) to the RRT or RRF of step (b),wherein Y is a leaving group selected from the group consisting of Cl,I, brosyloxy, mesyloxy, tosyloxy, trifluoroacetyloxy, andtrifluoromethansulfonyloxy, preferably, Cl.

The invention also encompasses a process of determining the amount ofthe compound of formula I in a sample comprising the compound of formulaI and the compound of formula II by a process comprising carrying out anHPLC with the compound of formula I as a reference standard.

The above process comprises: (a) measuring by HPLC the area under a peakcorresponding to a compound of formula I in a reference standardcomprising a known amount of the compound of formula I; (b) measuring byHPLC the area under a peak corresponding to a compound of formula I in asample comprising a compound of formula I and a compound of formula II;and (c) determining the amount of the compound of formula I in thesample by comparing the area of step (a) to the area of step (b),wherein Y is a leaving group selected from the group consisting of Cl,I, brosyloxy, mesyloxy, tosyloxy, trifluoroacetyoxyl, andtrifluoromethansulfonyloxy, preferably, Cl.

The HPLC method used to determine the presence and the presence and theamount of a compound of formula I

in a sample of a compound of formula II

comprises: (a) combining a sample of a derivative ofethyl-dihydrobenzofuran of formula I with a mixture ofacetonitrile:water in a ratio of about 1:1, to obtain a solution; (b)injecting the solution into a column, preferably, a 250×4.6 mm×0.5 μmC18 column; (c) eluting the sample from the column using a mixture ofacetonitrile and buffer as an eluent; and (d) measuring the amount ofthe compound of formula I in the sample with a UV detector, wherein Y isa leaving group selected from the group consisting of Cl, I, brosyloxy,mesyloxy, tosyloxy, trifluoroacetyloxy, and trifluoromethansulfonyloxy.

Preferably, the buffer used in this method is a phosphate buffer. Thephosphate buffer comprises an aqueous solution of K₂HPO₄ having a pH ofabout 9.

Typically, the sample is eluted through the column by gradient elution.Preferably, the eluent is a mixture of eluent A and buffer. Morepreferably, the sample is eluted through the column by gradient elutionunder the following conditions: At the time 0 minutes, the eluentcontains 50% of eluent A and 50% of buffer, at 20 minutes, the eluentcontains 70% of eluent A and 30% of buffer, and at 30 minutes, theeluent contains 70% of eluent A and 30% of buffer.

Preferably, the presence and content of the compound of formula I ismeasured at a wavelength of 215 nm.

The invention also encompasses a process for preparing darifenacinhydrobromide having less than 0.1% of oxidized Darifenacin and saltsthereof of the following formula

comprising: a) obtaining one or more samples of one of one or morebatches of a compound of formula II;

b) measuring the level of a compound of formula I

in one or more of the samples of one or more of the batches of step a);c) selecting a batch that has less than about 0.25% of the compound offormula I based upon the measurements of step b); andd) using the batch selected in step (c) to prepare the darifenacinhydrobromide having less than 0.1% of oxidized Darifenacin and saltsthereof, wherein Y is a leaving group selected from the group consistingof Cl, I, brosyloxy, mesyloxy, tosyloxy, trifluoroacetyloxy, andtrifluoromethansulfonyloxy; wherein n is either 0 or 1, wherein HA is anacid, preferably, HBr.

Typically, the one or more samples of compound of formula II of step (a)has less .than about 0.25% of the compound of formula I.

When the sample of the compound of formula II of step (a) has more thanabout 0.25% of the compound of formula I, according to the measurementin step (b), the sample may be purified, prior to performing step (c).The purification may be performed by at least one crystallizationprocess or by column chromatogrpahy.

Typically, the purified sample compound of formula II has a lower levelof compound of formula I than the level present before purification.Preferably, the compound of formula II sample of step (a) obtained afterpurification has less than about 0.25% of the compound of formula I.

The preparation of Darifenacin hydrobromide having less than 0.1% ofoxidized Darifenacin and salts thereof from the selected batch ofcompound of formula II, can be done for example, by the processdescribed before.

Unless specified otherwise, the darifenacin-HBr of step (d) of the aboveprocess may be in any physical form, including, for example, crystallineforms and amorphous forms.

The darifenacin-HBr having less than 0.10% of oxidized Darifenacin andsalts thereof may be formulated into pharmaceutical compositions for thetreatment of urinary incontinence reducing urgency and increasing urinevolume that the bladder can contain.

The invention encompasses a pharmaceutical composition comprisingdarifenacin hydrobromide having less than 0.10% of oxidized Darifenacinand salts thereof, and at least one pharmaceutically acceptableexcipient. Suitable excipients include, but are not limited to,diluents, carriers, fillers, bulking agents, binders, disintegrants,disintegration inhibitors, absorption accelerators, wetting agents,lubricants, glidants, surface active agents, flavoring agents, and thelike. Selection of excipients and the amounts to use can be readilydetermined by an experienced formulation scientist in view of standardprocedures and reference works known in the art.

The pharmaceutical composition can be formulated into a solid or aliquid dosage form for administration to a patient. Dosage formsinclude, but are not limited to, tablets, capsules, powders, syrups,suspensions, emulsions, injection preparations, and the like.

The invention also encompasses a process for preparing a pharmaceuticalcomposition comprising combining darifenacin hydrobromide having lessthan 0.10% of oxidized Darifenacin and salts thereof with at least onepharmaceutically acceptable excipient.

The invention also encompasses a method of treating urinary incontinencereducing urgency and increasing urine volume that the bladder cancontain comprising administering a therapeutically effective amount of apharmaceutical composition of darifenacin hydrobromide having less than0.10% of oxidized Darifenacin and salts thereof, and at least onepharmaceutically acceptable excipient to a patient in need thereof.

The invention also encompasses use of darifenacin hydrobromide havingless than 0.10% of oxidized Darifenacin and salts thereof in themanufacture of a pharmaceutical composition for the treatment of urinaryincontinence reducing urgency and increasing urine volume that thebladder can contain.

Having described the invention with reference to certain preferredembodiments, other embodiments will become apparent to one of ordinaryskill in the art from consideration of the specification. The inventionis further defined by reference to the following examples. It will beapparent to those of ordinary skill in the art that many modifications,both to materials and methods, may be practiced without departing fromthe scope of the invention.

EXAMPLES Analytical Methods

(a) Impurities determination in darifenacin-HBr by HPLC analysis:

Column & Phenyl-C6 150 mm × 4.6 mm × 5.0 μm Packing: Buffer: K₂HPO₄0.02M pH 9.0: 3.48 g of K₂HPO₄ in 1000 mL of water; Filter on a 0.45 μmfilter. Eluent A: acetonitrile/water- 90/10 Eluent B: Buffer GradientTime (min) % Eluent B % Eluent A  0 60 40 20 30 70 30 30 70 Equilibriumtime: 15 minutes Sample volume: 5.0 μL Flow Rate: 1.2 mL/min Detector:UV at 215 nm Column 35° C. temperature: Diluent H₂O:Acetonitrile (50:50)Typical retention times are:

Retention Time Relative Compound (minutes) Retention Time(S)-(1-carbamoyl-1,1- 2.6 0.19 diphenylmethyl)pyrrolidine (DIPAMP) offormula IV 5-(2-chloroethyl)-2,3- 12.6 0.91 dihydrobenzofuran (DBF-EtCl)of formula II Darifenacin 13.8 1.00 Oxidized darifenacin 16.0 1.16 Thedetection limit is 0.01%.(b) Impurities determination in 5-(2-chloroethyl)-2,3-dihydrobenzofuranof Formula II by HPLC analysis:

Column & C18 250 mm × 4.6 mm × 5.0 μm Packing: Buffer: K₂HPO₄ 0.02M pH7.0: 3.48 g of K₂HPO₄ in 1000 mL of deionized water, adjust pH at 7.0 ±0.2 with H₃PO₄ 15%(w/v). Filter on a 0.45 μm filter. Eluent A:Acetonitrile Eluent B: Buffer Gradient Time (min) % Eluent B % Eluent A 0 50 50 20 30 70 30 30 70 Equilibrium time: 8 minutes Sample volume:5.0 μL Flow Rate: 1.0 mL/min Detector: UV at 215 nm Column 35° C.temperature: Diluent H₂O:Acetonitrile (50:50)A typical Retention time of the 5-(2-chloroethyl)-2,3-dihydrobenzofiranof formula II is 12.7 min and a typical retention time of the oxidizedimpurity 1-(benzofuran-5-yl)ethyl chloride of formula I is 14.9 min. Thedetection limit is 0.01%.(c) TLC analysis

TLC is performed with silica gel as the stationary phase and a mixtureof hexane and toluene (95:5 vol:vol) as the eluent.

Example 1

Preparation of 2,3-dihydrobenzofuran-5-acetic acid methyl ester(DBFAcOMe)

98% H₂SO₄ (2 g, 0.02 mol)) was added to a solution of2,3-dihydrobenzofuran-5-acetic acid (DBFAcOH) (200g; 1.12 mol) inmethanol (500 ml) and the mixture was refluxed for 3hrs. After coolingto room temperature, NaHCO₃ (6.7 g, 0.11 mol) was added to the reactionmixture and the solvent was distilled off at atmospheric pressure (about440 ml) to give a light pink oily residue.

The oily residue was dissolved in toluene (250 ml) and washed withNaHCO₃ 6% (50 ml). After phase separation the solvent was eliminatedunder vacuum distillation obtaining an oily residue (227 g).

Example 2

Preparation of 5-(2-hydroxyethyl)-2,3-dihydrobenzofuran (DBFEtOH)

DBFAcOMe (227 g residue from Example 1) was dissolved in t-BuOH (600 ml)and NaBH₄ (46.8 g; 1.23 mol) was added. The resulting suspension waswarmed to reflux and methanol (100 ml) was added very slowly in about 6hrs followed by maintaining the reaction mixture at reflux. AfterMethanol addition, the reaction was maintained at reflux for half anhour (IPC revealed complete ester transformation). 400 ml of t-BuOH-MeOHmixture was distilled off at atmospheric pressure. Water (400 ml) wasadded to residue and distillation was continued till complete solventelimination. The reaction mixture was cooled to 70-75° C. and Toluene(300 ml) was added. Separated organic phase was washed with water (100ml) and NaCl 15% (100 ml).

After solvent elimination under vacuum distillation an oily residue(176.8 g; 1.076 mol) was obtained. The residue solidified uponcooling.).

Example 3

Preparation of 5-(2-chloroethyl)-2,3-dihydrobenzofuran (DBF-EtCl) offormula II

SOCl₂ (74.7 g; 0.63 mol) was added to a solution of DBF-EtOH (80 g; 0.48mol) in toluene (400 mL) maintaining the temperature below 25° C. Thereaction mixture was stirred at 60° C. for 14 h and then cooled to roomtemperature.

The mixture pH was adjusted to 10-11 by addition of 10% NaOH (about 480ml) while maintaining T<30° C. The organic phase was separated. Aqueousphase was extracted with Toluene ( 50 ml). Collected organic phases werewashed twice with H₂O (100 mL each) and anhydrified by vacuumdistillation. 20 g of Tonsil and 4,2 g of charcoal were added to theorganic phase, and stirred for 30 min at room temperature, filtered offand washed with toluene ( 2×30 ml). The decolorized solution wasconcentrated under vacuum to eliminate toluene. The residue wasdissolved in methanol (373 ml) and charcoal (2 g) was added. After 20min at 50-55° C. charcoal was filtered off and washed with hot methanol(2×10 ml). Decolorized solution was cooled at 20-30° C. and DBF-EtClcrystallized. To the suspension was added at 25-30° C. in about 60 min,water (280 ml) obtaining a sticky but stirrable suspension. After 1 hrat 20-25° C. solid was filtered and washed three times with MeOH-Water1:1 (20 ml each). Wet solid was dried at 35-40° C. for 15 hrs. Dryweight 81.8 g (0.45mol). Yield 92%).

Example 4 Preparation of Darifenacin Hydrobromide

Water (203 ml) Potassium carbonate (65 g) and DBF-EtCl (29.7 g) wereheated to 60-65° C. To the mixture3-(S)-(1-carbamoyl-1,1-diphenylmethyl)pyrrolidine tartrate ((S)-DIPAMPTartrate) (65 g) was added and the heterogeneous mixture was heated toreflux (101-102° C.) for 5 hrs. After cooling to 85-90° C., n-Butanol(325 ml) was added and after stirring phases were separated.

The organic phase was washed twice with water (160 ml each) and thenwater was removed from organic phase by vacuum distillation. N-Butanol(160 ml) and acetic anhydride (3.25 ml) were added and the solution wasstirred at 20-30° C. for 1 hr.

48% HBr (g 25.5) was added drop-wise and the water was removed by vacuumdistillation and DRF. HBr crystallised. Initial volume was restored byaddition of n-BuOH. Suspension was stirred at 15-20° C. for 2 hrs, thanproduct was recovered by filtration. The cake was washed with n-Butanol(3×30 ml) and wet solid (85-90 g) was crystallized without drying toobtain crude wet darifenacin hydrobromide.

The crude wet darifenacin hydrobromide (85 g), n-Butanol( 455 ml) andcharcoal (4.63 g) were warmed to reflux to obtain a solution. After halfan hour charcoal was filtered off keeping mixture at near reflux. Theclear solution at 100° C. was seeded with darifenacin hydrobromide andafter 30 min at 100° C. the solution was cooled to 15-20° C. in 2 hrs.The suspension was stirred at 15-20° C. for 2 hrs and then thedarifenacin hydrobromide was recovered by filtration. The filer cake waswashed with n-butanol (3×25 ml) to give wet purified darifenacinhydrobromide. The wet purified darifenacin hydrobromide was dried undervacuum at 50-55° C. for 10-12 hrs. Dry weight 59.2 g. Overall Yield77.2%).

Example 5

Synthesis of 5-(2-chloroethyl)-2,3-benzofuran (BF-EtCl) of Formula I

In a 500 ml reactor DBF-EtCl (30 g); NBS [N-Bromosuccinimide] freshlycrystallized (29.3 g) Dibenzoylperoxide (0.67 g) and CC14 (210 ml) wereloaded. Suspension was heated at gentle reflux (76° C.) for two hrs:vigorous gas evolution was observed. After two hrs reaction mixture wascooled and treated with Na₂S₂O₅ 15% (150 ml). After phase separation andwashings solvent was eliminated by under vacuum distillation obtaining ared oil (35 g). 20 g of oil were purified by silica gel columnchromatography (eluent: hexane). Fractions with HPLC purity higher then85% were collected and after solvent elimination 8.64 g of BF-EtCl wereisolated, HPLC purity 87.7%.).

Example 6 Preparation of (S)-Darifenacin Hydrobromide

A 50 ml reactor was loaded with 3-(S)-(+)-(1-carbamoyl-1,1-diphenylmethyl)pyrrolidine Tartrate (4 g, 9.29 mmoles),5-(2-chloroethyl)-2,3-dihydrobenzofuran (1.95 g, 10.68 mmoles),potassium carbonate (6.14 g, 44.42 mmoles), and water (12.5 ml), toobtain a heterogeneous mixture. The heterogeneous mixture was heated toreflux (103° C.) for 2.5 hours. After cooling dichloromethane, EtOAc orBuOAc (15 ml) were added, and, after stirring, the phases wereseparated. Acetic anhydride (0.5 ml) was added to the organic phase,and, after 1 hour at room temperature, the residual3-(S)-(+)-(l-carbamoyl-1,1-diphenylmethyl)pyrrolidine was transformedinto N-Acetyl derivative. The solvent was removed by distillation, andn-butanol (25 ml) was added to the residue. 48% hydrobromic acid (1.72g) was also added, and the residual DCM was removed under vacuumdistillation. In the case of EtOAc or BuOAc, distillation under vacuumis useful to eliminate water. Darifenacin hydrobromide crystallized,and, after cooling to room temperature, it was filtered and washed. (Wetsolid 4.17 g).

Example 7

Preparing Darifenacin-HBr from 5-(2-chloroethyl)-2,3-dihydrobenzofaranof Formula II

The process of Example 6 was repeated to obtain crude darfienacinhydrobromide, and the crude darifeancin hydrobromide was recrystallizedfrom n-butanol to obtain purified darifenacin hydrobromide. The purityof the purified darifenacin hydrobromide thus obtained was thenanalyzed. The results are summarized in the table below.

Level of oxidized Level of oxidized impurity (area impurity (w/w % % byHPLC) by HPLC) Tri- 5-(2-chloroethyl)- Oxidized al Components of Product2,3-benzofuran darifenacin 1 5-(2-chloroethyl)-2,3- 0.40 N/Adihydrobenzofuran of formula II darifenacin hydrobromide N/A 0.12(crude) darifenacin hydrobromide N/A 0.12 (purified) 25-(2-chloroethyl)-2,3- 0.50 N/A dihydrobenzofuran of formula IIdarifenacin hydrobromide N/A 0.19 (crude) darifenacin hydrobromide N/A0.20 (purified) 3 5-(2-chloroethyl)-2,3- 0.16 N/A dihydrobenzofuran offormula II darifenacin hydrobromide N/A 0.06 (crude) 45-(2-chloroethyl)-2,3- 0.16 N/A dihydrobenzofuran of formula IIdarifenacin hydrobromide N/A 0.06 (crude) darifenacin hydrobromide N/A0.07 (purified) 5 5-(2-chloroethyl)-2,3- 0.19 N/A dihydrobenzofuran offormula II darifenacin hydrobromide N/A 0.09 (crude) * N/A = notapplicable

Example 8

Preparing 5-(2-chloroethyl)-2,3-dihydrobenzofuran of Formula II in DMF,Toluene and in a Mixture of Dimethylformamide (DMF) and Toluene

Level of 2- Level of 5-(2- (benzofuran-5- chloroethyl)-2,3- yl)ethanolbenzofuran Temperature of formula of formula Solvent (° C.) V (area % byHPLC) I (area % by HPLC) DMF 20° C. nd 0.3 DMF 0-5° C. nd 0.44 Toluene/55° C. 0.01 1.15 DMF 99:1 Toluene 60° C. 0.03 0.21 Toluene 60° C. nd0.19 Toluene 60° C. nd 0.14 * nd = not determined

Example 9 Correlation Between the Levels of the Oxidized Impurities inthe Intermediates for Preparing Darifenacin Hydrobromide to the Level ofOxidized Darifenacin

Level of Level of Level of Level of Level of impurity impurity impurityimpurity impurity (w/w (area % by (area (area (area % % by HPLC) HPLC) %by HPLC) % by HPLC) by HPLC) Oxidized BF-AcOH BF-AcOMe BF-EtOH BF-EtCldarifenacin 0.18 0.17 0.16 0.18 0.09 0.50 0.53 0.47 0.30 0.49 * BF-AcOHis benzofuran-5-acetic acid; BF-AcOMe is benzofuran-5-methylester aceticacid; BF-EtOH is benzofuran-ethanol; and BF-EtCl is5-(2-chloroethyl)-benzofuran.

Example 10 Analysis of ENABLEX® Tablet

A commercially available tablet of ENABLEX® was analyzed by the HPLCmethod described above for analysis of darifenacin HBr. A sample ofENABLEX® was prepared by crushing a tablet of ENABLEX® into a powder,adding 7 ml of methanol to the powder to form a suspension, andsonicating the suspension for 10 minutes. The resulting solution wasfiltered and 0.5 ml of the filtered solution was diluted with 0.5 ml ofa 1:1 mixture of buffer (pH 7) and acetonitrile. The sample was thenanalyzed according to the HPLC method described above.

The analysis revealed that the ENABLEX® tablet contains a total amountof impurities of 1.07% area by HPLC, which distributes as follows: 0.03%area by HPLC of 3-(S)-( 1-carbamoyl- 1,1-diphenylmethyl)pyrrolidine,0.12% area by HPLC of oxidized darifenacin, and unidentified impuritiesin a total amount of 0.15% area by HPLC.

While it is apparent that the invention disclosed herein is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art. Therefore, it is intended that the appended claimscover all such modifications and embodiments as falling within the truespirit and scope of the present invention.

1. An HPLC method for determining the presence and level of oxidizeddarifenacin and salts thereof in a darifenacin hydrobromide samplecomprising: (a) combining a darifenacin hydrobromide sample with amixture of acetonitrile:water in a ratio of about 1:1, to obtain asolution; (b) injecting the solution into a 150×4.6 mm×5.0 μm Phenyl C6column; (c) eluting the sample from the column using a mixture ofacetonitrile:water in a ratio of 9:1 and buffer as an eluent; and (d)measuring the oxidized darifenacin content in the sample with a UVdetector.
 2. A process of determining the presence of a compound of thefollowing formula I

in a sample comprising the compound of formula I and a compound of thefollowing formula II

by a process comprising carrying out HPLC or TLC with the compound offormula I as a reference marker, wherein Y is a leaving group selectedfrom the group consisting of Cl, I, brosyl, mesyl, tosyl,trifluoroacetyl, and trifluoromethansulfonyl.
 3. The process of claim 2,comprising: (a) measuring by HPLC or TLC the relative retention timecorresponding to the compound of formula I in a reference marker sample;(b) determining by HPLC or TLC the relative retention time correspondingto the compound of formula I in a sample comprising a compound offormula I and a compound of formula II; and (c) determining the relativeretention time of the compound of formula I in the sample by comparingthe relative retention time of step (a) to the relative retention timeof step (b).
 4. The process of claim 3, wherein Y is Cl.
 5. A process ofdetermining the amount of a compound of the following formula I

in a sample comprising the compound of formula I and a compound of thefollowing formula II

by a process comprising carrying out an HPLC with the compound offormula I as a reference standard, wherein Y is a leaving group selectedfrom the group consisting of Cl, I, brosyl, mesyl, tosyl,trifluoroacetyl, and trifluoromethansulfonyl.
 6. The process of claim 5,comprising: (a) measuring by HPLC the area under a peak corresponding toa compound of formula I in a reference standard comprising a knownamount of the compound of formula I; (b) measuring by HPLC the areaunder a peak corresponding to a compound of formula I in a samplecomprising a compound of formula I and a compound of formula II; and (c)determining the amount of the compound of formula I in the sample bycomparing the area of step (a) to the area of step (b).
 7. The processof claim 6, wherein Y is Cl.
 8. The HPLC method of claim 3, comprising:(a) combining a sample of the compound of formula I with a mixture ofacetonitrile:water in a ration of about 1:1, to obtain a solution; (b)injecting the solution into a 250×4.6 mm×0.5 μm C18 column; (c) elutingthe sample from the column using a mixture of acetonitrile and buffer asan eluent; and (d) measuring the amount of the compound of formula I inthe sample with a UV detector at a wavelength of 215 nm.
 9. the methodof claim 8, wherein Y is Cl.
 10. The HPLC method of claim 6, comprising:(a) combining a sample of the compound of formula I with a mixture ofacetonitrile:water in a ratio of about 1:1, to obtain a solution; (b)injecting the solution into a 250×4.6 mm×0.5 μm C18 column; (c) elutingthe sample from the column using a mixture of acetonitrile and buffer asan eluent; and (d) measuring the amount of the compound of formula I inthe sample with a UV detector at a wavelength of 215 nm.
 11. The methodof claim 10, wherein Y is Cl.